It's hard to say for sure, experts say, given the many uncertainties about how complex climate dynamics will play out. But the likelihood is high for a rising incidence of a variety of disasters – including deadly heat waves and damaging superstorms that would periodically flood coastal cities and low-lying regions, potentially displacing millions of people.

As the consequences of massive global warming reverberated through ecosystems and societies, other possible outcomes include higher rates of disease, a rising swell of environmental refugees, extensive crop failure and widespread species extinctions.

With talks ongoing among global leaders in Paris this week, the pressure of such a catastrophic future offers hope that better policies and technological advancements will slow the rate of warming, helping to avert at least some of the potential catastrophe.

"The idea of an 8-degree warmer world and what that would mean is just unfathomable to me. It would just be so horrible," says Richard Seager, a climate scientist at the Lamont Doherty Earth Observatory of Columbia University in Palisades, N.Y. "I really hope we don't get there. And I would remain relatively confident that we will avoid that."

The focus of some of the most intense climate-change speculation -- and the source of some of the biggest debate -- is the relationship between warming-induced melting of Arctic ice and rising sea levels. It's a complicated process that has evaded attention until recently, Seager says, so there are still many uncertainties.

But the worst-case scenario isn't pretty. In a controversial new paper that is still undergoing peer review, an international group of scientists theorized that even just 2°C (about 4°F) of warming above preindustrial levels would lead to rapid melting in Greenland and Antarctica, leading to a dangerous rise in sea levels and an increasing number of powerful storms.

Some scientists have already warned that the 2°C mark is a tipping point beyond which the Earth won't be able to recover. By then, the Greenland ice sheet will be melting at a rate that cannot be stopped, argued Mark Lynas in his 2008 book "Six Degrees: Our Future on a Hotter Planet."

Rising seas don't necessarily cause problems on a daily basis, at least not at first. Instead, problems occur when powerful storms coincide with high tides in full seas, says Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo. That combination ups the chances for disasters like Hurricane Katrina in 2005, Superstorm Sandy in 2012, and Super Typhoon Haiyan in 2013. During some such events, subways flood. Homes topple. Cities crumble. Thousands die.

"If you imagine someone on the beach and the sea level slowly rises to his toes, then his ankles, then his knees -- that's not how it works," Trenberth says. Instead, the devastation is periodic, scattered and unpredictable. "It's not the same community time after time."

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In the United States, areas most at risk include Miami, New York, New Orleans, Boston and Tampa, according to a 2013 analysis published in Nature Climate Change. Even more imperiled are low-lying coastal regions in the highly populated developing world. Places like Bangladesh and many Pacific islands lack infrastructure and resources to protect themselves.

With every degree of warming, moisture in the atmosphere increases by about five percent, Trenberth adds, contributing more power to storms that can then dump massive amounts of snow or rain. Chances for flooding rise, even in inland areas.

And it's not just storms we have to worry about. Warmer global temperatures bring more frequent summer heat waves that can turn deadly when nighttime temperatures fail to drop. Along with less cooling in the winter, higher temperatures also allow diseases like West Nile Virus and pests like the pine bark beetle to persist and spread into temperate regions that used to be inhospitable to them. There may even be a rise in social strife and civil unrest.

As seasons and growing zones shift, another major concern is what will happen to food crops, as well as wild species of plants and animals. Those are changes we (and other species) might be able to adapt to, Trenberth says, but only if we manage to buy a little extra time. And outcomes in Paris could make a big difference.

"The rates of change matter enormously," he says. Two or more degrees of warming in the next 50 years wouldn't be good. But "if we can slow it down to 100 years, we'll be so much better off. If we can slow it down to 150 years, that's even better. What happens in Paris will determine when that happens."

You've heard a lot about how human-driven climate change will lead to hotter temperatures, cause sea levels to rise and make storms more intense. But it's projected to have plenty of other unpleasant and even disastrous effects as well. Here are 10 of them.
Scientists believe that rising temperatures will lead to increased evaporation of the Great Lakes' water, and precipitation won't make up the difference. That means we're likely to see declines in water levels over the next century, and one study predicts they may drop as much as 8 feet.

By altering the wild environment, climate change makes it easier for newly mutated microbes to jump between species, and it's likely that as a result, diseases will emerge and spread across the globe even more rapidly.

A recent Nature article reported that male Australian central bearded dragons have been growing female genitalia because of rising temperatures, a phenomenon that had not previously been observed in that species.

Rising sea levels are wiping out beaches all over the world already. Importing fresh sand and building them up again is only a temporary solution. To make matters worse, there's currently a sand shortage, due to demand from fracking, glass and cement making.

Warmer temperatures mean there will be more water vapor trapped in the atmosphere, leading to more lightning. A University of California-Berkeley study predicts that lightning strikes will increase by about 12 percent for every degree Celsius gained.

Wine grape harvests are being hurt. Regions that have historically supplied the world’s best wine will no longer be hospitable climates to grow wine grapes, according to research by the Environmental Defense Fund and others.

Coffee flavor depends upon really narrow conditions of temperature and moisture, and climate change is going to wreak havoc with that. Worse yet, as coffee growing regions become warmer, pests that couldn't survive in the past will ravage the crops. This is already being seen in Costa Rica, India and Ethiopia, which have experienced sharp declines in crop yields.